From the law just enunciated, we may learn th'at bodies upon the earth, moving with the earth, have the properties of bodies at rest with respect to all motions that aro to be estimated relatively to the earth : at least upon the supposition that the curvature of the motions of the earth is not sufficiently great to produce a sensible effect. We have then to inquire what is the natural state of matter on the earth f Can it preserve any motion of itself, or does every motion gradually slacken and die out, by the mere inability of matter to maintain it without the application of external causes / On this point wo have only strong presumptions, which would be by themselves insufficient Our first step would be to conclude, from what we actually see, that rest is the natural state of matter, and one to which It always approaches, however great a cause of motion be applied, unless that external cause, or some part. of it, be maintained. On looking further however we find that terrestrial matter, immediately on its being put in motion, encounter. causes of retardation. The resistance of the air, and the friction of the basis on which the substances rest, are easily shown to lessen the motion of bodies which encounter them. Tho more nearly these are removed, the longer doe. motion continue. It is certain then that these resistances contribute In a great degree to the destruction of motion; but it is not therefore to be immediately assumed that there is no other cause. If we grant that a perfectly smooth ball, lying upon in indefinitely extended plane without friction, and not in contact with any atmosphere, would move for a long time without any sensible diminution of the rate with which it was made to set out, we grant quite enough to explain all that wo see, without the necessity of sup posing that the motion would continue for ever. How then can wo establish the first law of motion (so called), which is thus Meted, that matter will retain its state of rest, or of motion, for any length of time, however great, until acted upon by some external cause ? We must here appeal to the results of the application of this Lew, which have never, in any one instance, exhibited any reason to suspect that it is only approximately true. Throughout the long period of astronomical history, no one of the heavenly bodies has shown any diminution of its motion, or any of the consequences which would arise if the motion had a tendency to wear itself out. Wo shall not here go into the details of these consequences ; the conclusion is, that the state which matter, independently of external bodies, has been created capable of maintaining, is not merely rest, but also uniform motion in a straight line; so that it has noemore tendency of itself to part with any of its velocity, nor to move slower or faster than it was first made to move, than it has to set itself from rest into motion. A great many, perhaps most, of the mistakes which have been made by writers against the Newtonian theory of attraction, have arisen from want of proper con ception of the 'ventral stale of matter. Maintenance of velocity and direction has been to them a proof of the existence of external causes maintained in action; whereas it proves nothing, but that there was at some time or other an external cause which acted for a longer or shorter time : the external cause steps in when the velocity changes, or the direction, or both, and not till then.
Properly considered, the immense number of different states which matter retains, namely, either absolute rest, or any degree of velocity whatsoever, is as wonderful and mysterious a Lew as that of the attraction of matter upon matter, without any apparent intermediate agent. That matter should, without any perceptible maintainer, keep
one rate of motion and ono direction until acted on from without, is as difficult to admit, as that the mere presence of other matter should change that motion and that direction. What should teach blind atoms to draw straight lines in preference to circles or spirals Have they the fundamental conceptions, according to some, or the powers of perception and inference, according to others, by which reasoning minds know or discover the simplicity of a straight line f These two consequences of observation, namely, the law of its existence, by which matter can retain certain states, if no other matter interfere, and that by which it can change the state of other matter, its own at the same time undergoing another change, should never be allowed to be separated. There are two classes of philosophical speculators (for no religious question need be allowed to enter), whose system introduces no difficulty into the details of mechanical philosophy which did not enter into its principles. The first consists of those theists who look upon the maintenance of the creation to be the con sequence of the same power as that which first created, and who consider that one moment's cessation of a sustaining power, of the same quality, so to speak, as the creative, would be the annihilation of all things : the second consists of atheists, who will of course find no more difficulty in the maintenance of the universe than in its first con struction. But a great confusion of ideas is introduced into all fundamental questions which relate to matter, by the existence of a sect which we suspect greatly to outnumber either of the former two, and whom we may mil believers in the Creator and not in the Main tainer. These, whatever they may think of the God of the moral world, imagine that the God of the material became inactive and quiescent as soon as matter was created, and endowed with certain powers, or made subject to certain laws. These laws, which are really their minor deities, carry on the business of the universe, and they can abstract the idea of God altogether from tho continuance of the existence of matter, though not from its first creation. Among them may be found many of the literal interpreters of the Mosaic account or THE EARTH], who hold strictly that the Creator "rested om his work," and left matter to its " laws," except on certain rare interpositions, Many of this sect have admitted the laws of motion, and, among others, the power of matter to maintain its motion, because there was an appearance of inactive sameness, or want of change, in the permanence of rest, or permanence of direction and velocity. But they have been startled by the entrance of attraction, and have disputed its possibility on account of the absence of second causes sufficient for its explanation : however clearly it might be shown that all the results of attraction are present among phenomena, they would not allow their first came to be awakened from the sleep in which it was their pleasure to suppose him plunged, so far as matter was concerned. Perhaps it is one of the roost singular mental aber rations which ever was manifested, that at the time of the appearance of the Newtonian doctrine, the first mechanical theory which rested on the maintainer of the creation, at least until (which has not yet happened) some good quiescent " second" cause was discovered—that doctrine was frequently charged with atheism.
If the earth were supposed to be fixed, we might obviously (though not obliged to do so) begin from matter at rest, and establish first that law of motion which usually stands first.